Though physical exertion and stress have been considered in a number of previous studies of pregnancy outcome, their potential influence on preterm birth and reduced fetal growth remains unresolved. We propose to evaluate the role of external stressors, perceived stress, enhancers and buffers of perceived stress, and physiologic markers of response to stress in relation to pregnancy outcome. We will enroll a cohort of 2,650 women who obtain prenatal care at Wake County Human Services Department/Wake Medical Center before the end of the 24th week of gestation. A detailed evaluation of domestic, occupational, and recreational physical activity patterns before and during pregnancy will be conducted. External stressors (life events, physical and emotional abuse, job stress, socioeconomic stress), perceived stress (impact of life events, discrimination, and safety), enhancers (anxiety, depression), buffers (social support, coping, religion), and physiologic markers of response to stress (plasma corticotropin releasing hormone (CRH), cortisol) will be evaluated througth the course of pregnancy. We will interview women at their first prenatal care visit, and again at weeks 18-24, 24-29, and 29-34 of gestation, and after delivery. In addition we will collect biological specimens to measure potential markers of physiologic response to stress, including salivary cortisol on all women and plasma CRH on 265 preterm delivery cases and a randomly sampled subcohort of 265 women. A race- and activity-stratified sample of 200 women from the cohort will be chosen for validation of the physical activity measures with a detailed diary of activity and a 4-day ergometer record. A separate sample of 100 women will be chosen to provide 24-hour urine specimens to measure catecholamines. To address key potential confounders, we will collect genital tract specimens at 24-29 weeks gestation to assess bacterial vaginosis and collect hair specimens at delivery to measure cocaine metabolites for preterm delivery cases and subcohort noncases only. Logistic recession modeling will examine the role of exertion and stress, with adjustment for potential confounders, in relation to the risk of preterm delivery (<37 weeks completed gestation) as the primary outcome, and secondarily, small-for-gestational age (SGA)births (<10th percentile of weight for gestational age). Substantial progress will be made in understanding the role of exertion and stress in pregnancy through the comprehensive prospective assessment at multiple points in gestation and detailed evaluation of potential confounders in a large, bi-racial population.